SQL Group按日期只选择1条记录

Question

I am trying to return only one record for the following table but not working. It return multiple record.Please advise, thank you

I suspect with the problem with groupby

CreateDate              Firstname EventID 
2013-05-13 18:11:35.187 Jack    0CD7B08A-0EAF-4515-9DE1-00FC6DB29A61
2013-05-13 18:11:35.310 Paul    16A584D5-E9B7-4617-8DC9-089C628E0ED5
2013-05-13 20:14:33.863 Craig   AAA21035-1377-443D-9BEE-0C0761534803

Here is the sql query for the result above:

 SELECT MAX (CreateDate) AS Create_Date, Firstname ,EventID
    FROM SessionsEvents
    WHERE TRN='0391588'

GROUP BY Firstname , TRN, EventID

Answer 1

Its Group data by FirstName after that with TRN and after that with EventID that TRN persent in your query and should be same in all resultset and FirstName, EventID columns have not same data for grouping and rows are separate in resultset then if you need maximum create date you should use TOP keyword for SQL Server:

SELECT TOP 1 MAX (CreateDate) AS Create_Date, Firstname ,EventID
FROM SessionsEvents
WHERE TRN='0391588'
GROUP BY Firstname , TRN, EventID

Answer 2

You don't want GROUP BY. You want TOP 1 with ORDER BY instead to get only the latest record by CreateDate.

SELECT TOP 1 CreateDate, Firstname ,EventID
FROM SessionsEvents
WHERE TRN='0391588'
ORDER BY CreateDate DESC

Answer 3

如果您对同一TRN有不同的FirstName或EventID ，您将获得多个组。